Lead frame and method of producing the same, and resin-encapsulated semiconductor device and method of producing the same

ABSTRACT

A resin-encapsulated semiconductor device includes a semiconductor chip, a plurality of inner leads that are connected to a group of electrodes of the semiconductor chip, respectively, and an encapsulating resin that encapsulates a connection part located between the semiconductor chip and the inner leads. Each of the inner leads includes a protruded portion provided on a surface thereof on an outer side relative to the periphery of the semiconductor chip. The protruded portion protrudes in a thickness direction and is provided with a step portion formed in its side portion. The group of electrodes of the semiconductor chip is connected to surfaces of inner portions of the inner leads located on an inner side relative to their protruded portions, through electroconductive bumps, respectively. The encapsulating resin encapsulates the semiconductor chip and the electroconductive bumps and is formed to expose surfaces of the protruded portions. The surfaces of the protruded portions that function as external terminals can be reduced in size and thereby the pitch between the external terminals can be reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin-encapsulated semiconductordevice with a lead frame. Particularly, it relates to a structure thatis suitable for achieving the reduction in thickness and the increase inspeed of elements, and a structure that is employed for achievingthree-dimensional mounting of a plurality of resin-encapsulatedsemiconductor devices, in a resin-encapsulated semiconductor devicecalled SIP (System In Package). Furthermore, the present inventionrelates to a lead frame used therein and the method of producing thesame as well as the method of producing a resin-encapsulatedsemiconductor device.

2. Related Background Art

Conventionally, a resin-encapsulated semiconductor device called “QFN(Quad Flat Non-leaded Package)”, only one side of which is encapsulatedwith an encapsulating resin, has been developed as a compact and thinresin-encapsulated semiconductor device. The following will describe theconventional QFN-type resin-encapsulated semiconductor device.

First of all, the following describes a lead frame used in aresin-encapsulated semiconductor device. FIG. 6 is a plan viewillustrating a conventional lead frame 1. This lead frame 1 has astructure in which a die pad 4 arranged substantially at the center ofan opening region 3 of a frame 2 is supported by hanging leads 5. Oneend of each of the hanging leads 5 is connected with each of the cornersof the die pad 4, while the other end thereof is connected with theframe 2. Further, the frame 2 is provided with a plurality of innerleads 6, which are arranged so that their ends face corresponding edgesof the die pad 4.

Next, the following describes a conventional resin-encapsulatedsemiconductor device employing the foregoing lead frame. FIGS. 7A and 7Bshow a conventional resin-encapsulated semiconductor device. FIG. 7A isa bottom view of a resin-encapsulated semiconductor device, and FIG. 7Bis a cross-sectional view of the device taken along line A–A1 shown inFIG. 7A. A semiconductor chip 7 is bonded to the die pad 4, and theframe 2 of the lead frame 1 (see FIG. 6) is cut away, so that the innerleads 6 are separated from one another. Electrodes 8 of thesemiconductor chip 7 are connected electrically with the surfaces of theinner leads 6 through thin metal wires 9, respectively. The surroundingsof the semiconductor chip 7 are encapsulated with an encapsulating resin10, with the bottom face of the die pad 4 and the bottom faces of theinner leads 6 being exposed. The bottom faces and side faces of theinner leads 6 are exposed at a bottom face and side faces of the package11, respectively, thereby forming external terminals 12.

Next, the following describes a method of producing theresin-encapsulated semiconductor device shown in FIGS. 7A and 7B. FIGS.8A to 8E illustrate steps of the production method by showing, like FIG.7B, the cross-sections taken along line A–A1 indicated in FIG. 7A.

First, a lead frame 1 is prepared as shown in FIG. 8A. This lead frame 1is the same as that shown in FIG. 6, though the illustration of theframe 2 (see FIG. 6) is omitted therein. The drawing shows a die pad 4on which a semiconductor chip is to be mounted, and one of a pluralityof inner leads 6 arranged so that their ends face the correspondingedges of the die pad 4. Next, as shown in FIG. 8B, a semiconductor chip7 is mounted on the die pad 4 of the lead frame 1 by bonding. Then, asshown in FIG. 8C, the semiconductor chip 7 is connected electricallywith surfaces of the inner leads 6 through thin metal wires 9.

Subsequently, as shown in FIG. 8D, the surroundings of the die pad 4,the surfaces of the inner leads 6, and the semiconductor device 7 arecovered with a molding die 13 to be encapsulated with an encapsulatingresin. Thereafter, as shown in FIG. 8E, the package 11 that has beenencapsulated with the encapsulating resin 10 is taken out of the moldingdie. Thus, a resin-encapsulated semiconductor device is completed inwhich the bottom faces and outer side faces of the inner leads 6 arearranged in the bottom of the package 11 to serve as external terminals12 (see, for instance, JP2000-307049A).

However, the conventional resin-encapsulated semiconductor device asdescribed above is very thick as a whole since the thin metal wires areused for connecting the electrodes of the semiconductor chip with theinner leads, and hence, there are limits to the reduction in thicknessof the device. Furthermore, since no consideration has been given to thesize of the exposed faces of the inner leads that form the externalterminals, the above-mentioned structure was not suitable for reducingthe size of the external terminals and the pitch of the externalterminals, i.e. the distance between the external terminals.

In addition, in a situation where high-speed signals or high-frequencysignals operate, loss of signals in the thin metal wires becomes aproblem, which prevents the semiconductor chip from fully functioning.

Moreover, since the external terminals are exposed only at the bottomface of the resin-encapsulated semiconductor device, when a plurality ofresin-encapsulated semiconductor devices are stacked on top of eachother, no electric connection can be established between the devicesthrough their external terminals. Thus, it is difficult to implement thethree-dimensional packaging.

SUMMARY OF THE INVENTION

A lead frame of the present invention includes a frame, and a pluralityof inner leads extending inward from the frame, wherein the inner leadincludes a protruded portion provided on a surface of its outer portion,the protruded portion protrudes in a thickness direction, and a stepportion is formed in a side portion of the protruded portion.

In this lead frame, the protruded portion has a reduced cross-section onits tip side relative to the step portion. Hence, the tip face of theprotruded portion that functions as an external terminal has a reducedarea, which allows a reduced pitch to be obtained between the tip facesof the protruded portions of the respective inner leads.

A method of producing a lead frame of the present invention includes:forming a structure including a frame and a plurality of inner leadsextending inward from the frame; half-etching or pressing a part of thesurface of the inner leads to form a protruded portion on the surface;and then carrying out half-etching or pressing again from thesurroundings of the surface of the protruded portion to form a stepportion in its side portion. With this method, the step portion can beformed easily in the protruded portion.

A resin-encapsulated semiconductor device of the present inventionincludes: a semiconductor chip; a plurality of inner leads that arearranged along a periphery of the semiconductor chip and are connectedto a group of electrodes of the semiconductor chip, respectively; and anencapsulating resin that encapsulates a connection part located betweenthe semiconductor chip and the inner leads. A part of each of the innerlead is exposed from the encapsulating resin to form an externalterminal. The inner lead includes a protruded portion that protrudes inthe thickness direction and is provided on its surface on the outer siderelative to the periphery of the semiconductor chip. The protrudedportion has a step portion formed in its side portion. The group ofelectrodes of the semiconductor chip is connected to the surfaces ofinner portions of the inner leads located on the inner side relative totheir protruded portions, through electroconductive bumps, respectively.The encapsulating resin is formed so as to encapsulate the semiconductorchip and the electroconductive bumps and to expose the surfaces of theprotruded portions.

In this configuration, the protruded portion of the inner lead has areduced cross-section on its tip side relative to the step portion.Hence, the tip face of the protruded portion that functions as anexternal terminal has a reduced area, which allows a reduced pitch to beobtained between the tip faces of the protruded portions of therespective inner leads.

In a method of producing a resin-encapsulated semiconductor device ofthe present invention, a lead frame is employed that includes a frameand a plurality of inner leads extending inward from the frame. In thelead frame, the inner lead has a protruded portion on the surface of itsouter portion, and the protruded portion protrudes in a thicknessdirection with a step portion formed in a side portion of the protrudedportion. The method includes steps of: forming first electroconductivebumps on the surfaces of the inner leads on the inner side relative totheir protruded portions; stacking a second semiconductor chip with asmaller size than that of a first semiconductor chip, on the surface ofthe first semiconductor chip, and electrically connecting a first groupof electrodes of the first semiconductor chip with a group of electrodesof the second semiconductor chip through second electroconductive bumps;electrically connecting the first electroconductive bumps with a secondgroup of electrodes of the first semiconductor chip formed on the outerside relative to the region of the first semiconductor chip to which thesecond semiconductor chip has been connected; and encapsulating theregion including the surfaces of the first and second semiconductorchips and the first and second electroconductive bumps using anencapsulating resin, with the surfaces of the protruded portions beingsubstantially in the same plane as the outer face of the encapsulatingresin and being exposed from the encapsulating resin.

Another method of producing a resin-encapsulated semiconductor device ofthe present invention employs the same lead frame as that used in theabove-mentioned production method. This method includes steps of formingfirst electroconductive bumps on the surfaces of the inner leads on theinner side relative to their protruded portions; stacking a secondsemiconductor chip with a smaller size than that of a firstsemiconductor chip, on the surface of the first semiconductor chip, andelectrically connecting a first group of electrodes of the firstsemiconductor chip with a group of electrodes of the secondsemiconductor chip through second electroconductive bumps; electricallyconnecting the first electroconductive bumps with a second group ofelectrodes of the first semiconductor chip formed on the outer siderelative to the region of the first semiconductor chip to which thesecond semiconductor chip has been connected; and encapsulating theregion including the surfaces of the first and second semiconductorchips and the first and second electroconductive bumps using anencapsulating resin.

In this production method, the tip faces of the protruded portions ofthe inner leads, which function as external terminals, each have a smallarea. This allows a reduced pitch to be obtained between the tip facesof the protruded portions of the respective inner leads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view illustrating a lead frame according to anembodiment of the present invention; and FIG. 1B is a cross-sectionalview of the lead frame taken along line B–B1 shown in FIG. 1A.

FIG. 1C is a cross-sectional view of an improved structure of the leadframe according to the same embodiment.

FIG. 2A is a plan view illustrating a resin-encapsulated semiconductordevice according to an embodiment of the present invention; FIG. 2B is aside view thereof; FIG. 2C is a bottom view thereof; and FIG. 2D is across-sectional view thereof taken along line C–C1 shown in FIG. 2A.

FIG. 3A is a plan view illustrating an improved structure of theresin-encapsulated semiconductor device according to the sameembodiment.

FIGS. 3B and 3C are cross-sectional views of the resin-encapsulatedsemiconductor device taken along line D–D1 and line E–E1 shown in FIG.3A, respectively.

FIG. 3D is a cross-sectional view illustrating a state where a pluralityof resin-encapsulated semiconductor devices according to the embodimentare stacked on top of each other.

FIGS. 4A to 4D are cross-sectional views illustrating respective stepsof a method of producing the resin-encapsulated semiconductor deviceshown in FIGS. 2A to 2D.

FIGS. 5A to 5E are cross-sectional views illustrating respective stepsof another method of producing the resin-encapsulated semiconductordevice.

FIG. 6 is a plan view illustrating a conventional lead frame.

FIG. 7A is a plan view illustrating a conventional resin-encapsulatedsemiconductor device; and FIG. 7B is a cross-sectional view thereoftaken along line A–A1 shown in FIG. 7A.

FIGS. 8A to 8E are cross-sectional views illustrating respective stepsof a method of producing the conventional resin-encapsulatedsemiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

In the resin-encapsulated semiconductor device of the present invention,the step portion is formed as a portion with two steps or more. Withsuch a step portion, in the encapsulating step, when a resin tape isinterposed between a molding die and the lead frame, the encapsulatingresin tends not to flow into between the resin tape and the protrudedportions of the lead frame. As a result, the possibility is reduced thatthe encapsulating resin adheres to the surfaces of the protrudedportions. Accordingly, the surfaces of the protruded portions functionas external terminals more reliably.

In the resin-encapsulated semiconductor device of the present invention,the semiconductor chip may be composed of a first semiconductor chip anda second semiconductor chip that is stacked on the surface of the firstsemiconductor chip and has a smaller size than that of the firstsemiconductor chip. In this case, the protruded portions of theplurality of inner leads are located on the outer side relative to theperiphery of the first semiconductor chip. The first group of electrodesof the first semiconductor chip is connected with the surfaces of theinner portions of the inner leads located on the inner side relative totheir protruded portions, through the first electroconductive bumps,respectively. The second semiconductor chip is disposed within theregion surrounded by inner ends of the plurality of inner leads and isconnected electrically with the second group of electrodes of the firstsemiconductor chip through the second electroconductive bumps. Theencapsulating resin encapsulates the surfaces of the first and secondsemiconductor chips and the first and second electroconductive bumps.

In the resin-encapsulated semiconductor device of the present invention,it is preferable that the surfaces of the protruded portions aresubstantially in the same plane as the outer face of the encapsulatingresin. Furthermore, it is preferable that the back face of the firstsemiconductor chip and the outer face of the encapsulating resin aresubstantially in the same plane. It also is preferable that the backfaces of the inner leads and the outer face of the encapsulating resinare substantially in the same plane. With these configurations, aplurality of resin-encapsulated semiconductor devices can be stackedstably on top of each other.

Moreover, the inner lead preferably is tilted upward, i.e. to the sideon which the protruded portion is provided, toward the inner end of theinner lead. This allows the back face of the inner lead located on itsouter end side to protrude relative to its inner portion and thereby tobe exposed easily in the encapsulating step to form the externalterminal without fail. It also is preferable that ball electrodes areformed on the protruded portions. This makes it possible to improve thereliability of electric connection of the device with a mounting board.Furthermore, another configuration may be employed in which aninsulating thin film is formed on a part of the surface of the protrudedportions of the inner leads and the part where the insulating thin filmhas not been formed functions as the external terminal. With thisconfiguration, electrical leakage can be prevented even when the deviceis mounted directly on a circuit board. Moreover, even when a bendingstress is transmitted from the circuit board, the bending stress can beabsorbed by the ball electrodes.

Further, a resin-encapsulated semiconductor device can be obtained inwhich a plurality of resin-encapsulated semiconductor devices with anyof the above-mentioned configurations are stacked on top of each other,and adjacent pairs of them are electrically connected to each other withthe back faces of the inner leads of one being electrically connectedwith the surfaces of protruded portions of the other. With thisconfiguration, a plurality of resin-encapsulated semiconductor devicescan be stacked easily on top of each other. Accordingly, theresin-encapsulated semiconductor device can perform various functionswhile requiring a small mount area. In this case, threeresin-encapsulated semiconductor devices or more can be stacked on topof each other.

In the encapsulating step of the method of producing aresin-encapsulated semiconductor device according to the presentinvention, after the encapsulating step, a portion sticking out from theencapsulating resin of the inner leads can be cut off and thereby thestructure encapsulated with the resin can be separated from the frame.Preferably, the encapsulating resin is fed with a resin sheet being inclose contact with at least the protruded portions. This can prevent theencapsulating resin from adhering to the surfaces of the protrudedportions in the encapsulating step and thereby allows the surfaces ofthe protruded portions to be exposed reliably.

Hereinafter, embodiments of the present invention are described indetail with reference to the drawings. First, the description isdirected to the configuration of a lead frame. FIG. 1A is a plan viewillustrating a lead frame 14 according to the present embodiment, andFIG. 1B is a cross-sectional view of the lead frame taken along lineB–B1 shown in FIG. 1A.

The lead frame 14 is formed of a metal plate such as, for example, onemade of a copper material, a 42-alloy, or the like. A frame 15 has athickness of 100 μm to 300 μm. A plurality of inner leads 16 are formedto extend inward from the frame 15. Each of the inner leads 16 has aprotruded portion 17 on its surface on the outer side. In thisconnection, the surface of the inner lead 16 denotes the face opposing asemiconductor chip to be mounted, i.e. a face on which anelectroconductive bump is formed to establish the electric connectionwith electrodes of the semiconductor chip. On the inner side relative tothe protruded portion 17, an inner end portion is formed of a thin innerpart 16 a. The protruded portion 17 is provided with step portions 18that may be formed in its side portions to have half the thickness ofthe frame 15. The thickness of the step portions 18, however, may be setsuitably. In the present embodiment, the thickness of the lead frame 14is set, for example, at 150 μm, and the step portions 18 each may beprovided with two steps or more.

As shown in FIG. 1C, each inner lead 16 may be tilted upward, i.e. tothe side on which the protruded portion protrudes, toward an inner endof the inner portion 16 a. Thereby the back face of the inner portion 16a is recessed from the back face of the inner lead 16 located on theouter end face side. In other words, the back face of the inner lead 16located on the outer end face side protrudes beyond the back face of theinner portion 16 a.

Next, the description is made with respect to an outline of the methodof producing the lead frame 14 according to the present embodiment.First, a structure with a uniform thickness is produced that includes aframe and a plurality of inner leads extending inward from the frame.Thereafter, a part of the surface of each inner lead is half-etched orpressed and thereby a protruded portion is formed on the surface of theinner lead. Then, further half-etching or pressing is carried out fromthe surroundings of the surface of the protruded portion to provide theside portions of the protruded portion with a step portion.

The following description is directed to a resin-encapsulatedsemiconductor device of the present embodiment. FIG. 2A is a plan viewillustrating a resin-encapsulated semiconductor device; FIG. 2B is aside view thereof; FIG. 2C is a bottom view thereof; and FIG. 2D is across-sectional view thereof taken along line C–C1 shown in FIG. 2A.This resin-encapsulated semiconductor device includes the lead frameshown in FIGS. 1A and 1B, and a first semiconductor chip 19 and a secondsemiconductor chip 25 that are mounted on the lead frame.

FIG. 2A shows a state where the back face of the first semiconductorchip 19 and the surfaces of the protruded portions 17 of the inner leads16 are exposed from an encapsulating resin 26. FIG. 2B shows a statewhere outer end faces of the inner leads 16 are exposed from theencapsulating resin 26. FIG. 2C illustrates a state where the back faceof the second semiconductor chip 25 and the back faces of the innerleads 16 are exposed from the encapsulating resin 26.

As shown in FIG. 2D, first electroconductive bumps 21 are formed onfirst electrodes 20 arranged in the peripheral portion of the firstsemiconductor chip 19. An inner portion 16 a of each inner lead 16extends inward relative to the periphery of the first semiconductor chip19, and is connected to a corresponding one of the firstelectroconductive bumps 21. Step portions 18 and the protruded portion17 of each inner lead 16 are disposed on the outer side relative to theperiphery of the first semiconductor chip 19. A ball electrode 22 madeof solder or the like to serve as an external electrode is provided onthe surface of the protruded portion 17. The tip end of the externalelectrode 22 protrudes beyond the back face of the first semiconductorchip 19.

Within the region surrounded by inner ends of the plurality of the innerleads 16 is disposed the second semiconductor chip 25 that has a smallersize than that of the first semiconductor chip 19. On the inner siderelative to the first electrodes 20 disposed on the surface of the firstsemiconductor chip 19 are formed second electrodes 23 facing the secondsemiconductor chip 25. The second electrodes 23 of the firstsemiconductor chip 19 are connected electrically with electrodes 25 a ofthe second semiconductor chip 25 through second conductive bumps 24. Thesurfaces of the first and second semiconductor chips 19 and 25 as wellas the first and second electroconductive bumps 21 and 24 areencapsulated with an encapsulating resin 26 in such a manner thatsurfaces of the protruded portions 17 of the inner leads 16 are exposed.The surfaces of the protruded portions 17 and the back face of the firstsemiconductor chip 19 are substantially in the same plane as the outerface of the encapsulating resin 26. Furthermore, the back faces of theinner leads 16 and the outer face of the encapsulating resin 26 aresubstantially in the same plane.

In the present embodiment, the formation of the step portions 18 allowseach protruded portion 17 disposed on the tip side to have a reducedcross-section. Accordingly, the tip faces of the protruded portions 17that function as external terminals each have a reduced area, whichallows a reduced pitch to be achieved between the tip faces of theprotruded portions 17.

With the ball electrodes 22 provided on the protruded portions 17, evenwhen bending stress is transmitted from a circuit board to theresin-encapsulated semiconductor device mounted on the circuit board,the bending stress can be absorbed by the ball electrodes 22.

Each inner lead 16 may be tilted upward as shown in FIG. 1C, i.e. to theside on which the protruded portion protrudes, toward an inner end ofthe inner portion 16 a. Thereby, the back face of the inner lead 16located on the outer end face side protrudes relative to the back faceof the inner portion 16 a and thus can be exposed easily from the outerface of the encapsulating resin 26 in the encapsulating step. Thisallows the device to establish a reliable electric connection with acircuit board and the like.

Furthermore, as shown in FIGS. 3A to 3C, an insulating thin film 33 maybe formed on a part of the surface of the protruded portion 17 of eachinner lead 16. FIG. 3A is a plan view illustrating a resin-encapsulatedsemiconductor device. FIGS. 3B and 3C are cross-sectional views of thedevice taken along line D–D1 and line E–E1 shown in FIG. 3A,respectively. As shown in FIGS. 3A and 3C, the insulating thin film 33has an aperture 33 a. The part of the surface of the protruded portion17 in the aperture 33 a where the insulating thin film 33 is not formedcan be used as the external terminal. This can prevent electric leakagefrom occurring even when the device is mounted directly on a circuitboard.

Moreover, a small convex part may be formed on a part of the surface ofeach inner lead 16 that comes to contact with the firstelectroconductive bump 21. In this case, the convex part bites into thefirst electroconductive bump 21 to establish the electrical contacttherebetween, and this ensures a stable electric connection between thefirst electroconductive bump 21 and the inner lead 6. The convex partmay be formed to have a concave part at its tip.

Next, the description is directed to the case where a plurality ofresin-encapsulated semiconductor devices with the aforementionedconfiguration are stacked on top of each other. FIG. 3D is across-sectional view illustrating the state where a plurality ofresin-encapsulated semiconductor devices 27 to 30 are stacked on top ofeach other, and adjacently stacked pairs of them are electricallyconnected with each other.

The surfaces of the protruded portions 17 of the inner leads 16 providedin the resin-encapsulated semiconductor device 29 disposed on the lowerside are connected to the back faces of the inner leads 16 provided inthe resin-encapsulated semiconductor device 28 disposed on the upperside, through the ball electrodes 22 made of solder. Thus, according tothe present embodiment, a plurality of resin-encapsulated semiconductordevices can be stacked on top of each other and easily can be connectedto each other electrically. Accordingly, a resin-encapsulatedsemiconductor device of a high-density packaging type can be obtainedthat performs various functions while requiring a mount area needed forone resin-encapsulated semiconductor device. The number of theresin-encapsulated semiconductor devices to be stacked on top of eachother can be selected suitably.

The following description is directed to a method of producing theresin-encapsulated semiconductor device with the aforementionedconfiguration. First, the description is made about a first productionmethod according to the present embodiment with reference to FIGS. 4A to4D.

As shown in FIG. 4A, the lead frame 14 shown in FIG. 1 is prepared.Next, as shown in FIG. 4B, first electroconductive bumps 21 are formedon the surfaces of the inner portions 16 a of the inner leads 16.Separately, a first semiconductor chip 19 and a second semiconductorchip 25 are stacked on top of each other, and second electrodes 23 ofthe first semiconductor chip 19 are connected electrically withelectrodes 25 a of the second semiconductor chip 25 through secondelectroconductive bumps 24. Subsequently, the structure with the firstsemiconductor chip 19 and the second semiconductor chip 25 that arestacked on top of each other is combined with the lead frame 14 as shownin the drawing. First electrodes 20 of the first semiconductor chip 19and first electroconductive bumps 21 formed on the inner leads 16 areelectrically connected correspondingly to each other.

Next, as shown in FIG. 4C, the lead frame 14 and the first and secondsemiconductor chips 19 and 25 are inserted into a molding die 31, andthen the surfaces of the first and second semiconductor chips 19 and 25and the first and second electroconductive bumps 21 and 24 areencapsulated with an encapsulating resin 26 (see FIG. 4D). Subsequently,as shown in FIG. 4D, a portion stuck out from the encapsulating resin ofthe inner leads 16, which is not shown in the drawing, is cut off andthereby the resin-encapsulated structure is separated from the frame.

In the encapsulating step shown in FIG. 4C, the surfaces of theprotruded portions 17 are exposed from the encapsulating resin 26 insuch a manner as to be substantially in the same plane as the outer faceof the encapsulating resin 26, as shown in FIG. 4D. In this step, theencapsulating resin 26 is injected into the molding die 31 with a resinsheet 32 being in close contact with the back face of the firstsemiconductor chip 19 and the surfaces of the protruded portions 17 ofthe lead frame 14. This prevents the encapsulating resin 26 from beingformed on the surfaces of the protruded portions 17. Accordingly, anadequate electric connection is secured between the protruded portions17 and wiring electrodes of a mounting board.

Next, a second method of producing a resin-encapsulated semiconductordevice is described with reference to FIGS. 5A to 5E. First, as shown inFIG. 5A, the lead frame 14 shown in FIG. 1 is prepared. Subsequently, asshown in FIG. 5B, first electrodes 20 of a first semiconductor chip 19and the inner portions 16 a of the inner leads 16 are electricallyconnected to each other through first electroconductive bumps 21.Thereafter, as shown in FIG. 5C, second electrodes 23 of the firstsemiconductor chip 19 and electrodes 25 a of a second semiconductor chip25 are connected electrically to each other through secondelectroconductive bumps 24.

Then, as shown in FIG. 5D, the surfaces of the first and secondsemiconductor chips 19 and 25 and the first and second electroconductivebumps 21 and 24 are encapsulated with an encapsulating resin 26 (seeFIG. 5E) using a molding die 31 and a resin sheet 32. Subsequently, asshown in FIG. 5E, a portion stuck out from the encapsulating resin ofthe inner leads 16, which is not shown in the drawing, is cut off andthereby the resin-encapsulated structure is separated from the frame. Inthe encapsulating step shown in FIG. 5D, the surfaces of the protrudedportions 17 are exposed from the encapsulating resin 26 in such a manneras to be substantially in the same plane as the outer face of theencapsulating resin 26 as shown in FIG. 5E.

According to the production methods of the present embodiment describedabove, a thin resin-encapsulated semiconductor device with a thicknessof 0.8 mm or less can be produced easily. Accordingly, theresin-encapsulated semiconductor device can be contained in a thinstandardized PC card with each side thereof being mounted on a mountboard.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A lead frame, comprising: a frame; and a plurality of inner leads,extending inward from the frame, wherein the inner lead includes aprotruded portion provided on a surface of its outer portion, theprotruded portion protrudes in a thickness direction so as to have athickness larger than an inner portion of the inner lead, and at leastone step portion is formed on each of an inner and outer side portionsof the protruded portion.
 2. The lead frame according to claim 1,wherein each of the inner leads is tilted to a side on which theprotruded portion is formed toward an inner end of the inner lead. 3.The lead frame according to claim 1, wherein a back face of each of theinner leads, just below the protruded portion, forms the lowest part ofthe inner leads.
 4. The lead frame according to claim 2, wherein a backface of each of the inner leads, just below the protruded portions,forms the lowest part of the inner leads.
 5. A resin-encapsulatedsemiconductor device, comprising: a semiconductor chip having a group ofelectrodes; a plurality of inner leads that are arranged along aperiphery of the semiconductor chip and are connected to the group ofelectrodes of the semiconductor chip, respectively; and an encapsulatingresin that encapsulates a connection part located between thesemiconductor chip and the inner leads, with a part of each of the innerleads being exposed from the encapsulating resin to form an externalterminal, wherein the inner lead includes a protruded portion providedon a surface thereof on an outer side relative to the periphery of thesemiconductor chip, the protruded portion protruding in a thicknessdirection so as to have a thickness larger than the inner portion of theinner lead with at least one step portion formed on each of the innerand the outer side portions of the protruded portion, the group ofelectrodes of the semiconductor chip is connected to surfaces of innerportions of the inner leads located on an inner side relative to theirprotruded portions, through electroconductive bumps, respectively, andthe encapsulating resin encapsulates the semiconductor chip and theelectroconductive bumps and is formed to expose surfaces of theprotruded portions.
 6. The resin-encapsulated semiconductor deviceaccording to claim 5, wherein the semiconductor chip includes a firstsemiconductor chip and a second semiconductor chip that is stacked on asurface of the first semiconductor chip and has a smaller size than thatof the first semiconductor chip, the protruded portions of the pluralityof inner leads are located on an outer side relative to a periphery ofthe first semiconductor chip, a first group of electrodes of the firstsemiconductor chip is connected with the surfaces of the inner portionsof the inner leads located on the inner side relative to their protrudedportions, through first electroconductive bumps, respectively, thesecond semiconductor chip is disposed within a region surrounded byinner ends of the plurality of inner Leads and is connected electricallywith a second group of electrodes of the first semiconductor chipthrough second electroconductive bumps, and the encapsulating resinencapsulates surfaces of the first and second semiconductor chips andthe first and second electroconductive bumps.
 7. The resin-encapsulatedsemiconductor device according to claim 5, wherein the surfaces of theprotruded portions and an outer face of the encapsulating resin aresubstantially in the same plane.
 8. The resin-encapsulated semiconductordevice according to claim 5, wherein a back face of the semiconductorchip and an outer face of the encapsulating resin are substantially inthe same plane.
 9. The resin-encapsulated semiconductor device accordingto claim 5, wherein back faces of the inner leads and an outer face ofthe encapsulating resin are substantially in the same plane.
 10. Theresin-encapsulated semiconductor device according to claim 5, whereinthe inner lead is tilted gradually to a side on which the protrudedportion is formed, toward an inner end of the inner lead.
 11. Theresin-encapsulated semiconductor device according to claim 5, wherein aplurality of ball electrodes are formed on the protruded portions. 12.The resin-encapsulated semiconductor device according to claim 5,wherein an insulating thin film is formed on a part of the surface ofthe protruded portions of the inner leads, and a part of the surface ofthe protruded portion where the insulating thin film has not been formedfunctions as an external terminal.
 13. A resin-encapsulatedsemiconductor device, wherein a plurality of resin encapsulatedsemiconductor devices according to claim 5 are stacked on top of eachother, and in adjacent pairs, back faces of inner leads of one areconnected electrically with surfaces of protruded portions of an other.14. The resin-encapsulated semiconductor device according to claim 13,wherein at least three resin-encapsulated semiconductor devices arestacked on top of each other.